Or one might be up the proverbial s***y moonlet without a paddle on an unmoonletlit night.
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Can I apply a similar logic to any body (my own as an example)?Is the mistake to imagine the field as a "thing" rather than a series of measurements?
No. The reason is that it is a thing ie a series of values in an area of space. It can be considered as an object which can be discussed, manipulated mathematically etc.
However, I suspect you are asking whether it has a life of its own. Well, take a gravitational field, would it exist if there were no mass in the universe? It would certainly have zero magnitude. Despite that, we can still consider the concept of a gravitational field even if there is no mass.
Is the mistake to imagine the field as a "thing" rather than a series of measurements?A field is a series of measurements made in space - most have a zero value in the quiescent state. Along comes an electron carrying a charge, value of electron field is disturbed and increases to that of the electron charge; electron passes by, disturbance goes, value of field drops to zero.Quote from: JeffreyThese do have a source within the particles that generate them.
Therein lies my problem.
If a particle is a disturbance in a field, how can a particle exist without a field?
If a field has to exist before it can be disturbed; how can the disturbance be the source of the field?
I thought a photon only became a photon when the light wave interacted with something.Quote from: Going going…..A photon does not slow down unless it interacts with something ie a material …..
If a photon reacts with something, doesn’t it cease being a photon?
The "in a vacuum" qualification is important to relativity. All formulas and equations relate to c. c is the speed at which light will travel through a vacuum. The fact that light travels slower through water will not result in the effects of Relativity being any different, because even in water c remains unchanged even if the actual speed of the light through the water has changed.Is it the case that light does travel at c in water? Is it a case of stop-start with the stops occurring every time the light wave interacts with the medium and the starts being periods where it continues at the speed of c?
Light isn't the issue at all. it is the speed c. Light in a vacuum happens to travel at this speed, so it makes a convenient reference.
Did he ever come around to thinking of it as a geometry?No. In fact he wrote to Lincoln Barnett on June 19, 1948, sayingQuoteI do not agree with the idea that general relativity is geomterizing physics of a gravitational field. The concepts of physics have always been geometrical concepts and I cannot see why the gik field should be called more geometrical han f.i. the electromagnetic field or the distance between bodies in Newtonian mechanics. The notion probably comes from the fact that the mathematical origin of the gik[/dub] field is the Gauss-Riemann theory of the metrical continuum which we are wont to look at as part of geometry. I am convinced, however, that the distinction between geometrical and other kinds of fields is not logically founded.
thanks. I will give it a listen if I get time.Quote from: Bill SAre there any educated guesses at all as to the ratio between the observed and the unobserved universe? Could it be an infinite ratio?That question comes up later in the same interview with Prya Nataranjan.
As I recall, "an infinite universe is still on the menu".
Taking the piss is different from taking a piss (although you could do both at the same time)Quote from: dead catAre you taking the piss, in what universe does matter get stuck outside the event horizon of a black hole. Do you have a citation?I heard that phrase "Are you taking a piss?" in the movie Kingsman: The Secret Service. What does it mean? I live in New England. Is that phrase a British thing?
Citation? Sure On the Influence of Gravitation on the Propagation of Light by Albert Einstein, Annalen der Physik[/b], 35, 1911.
Interesting stats, Evan. Multiply this by the number (and size) of galaxies and you have the number for the Universe.Are there any educated guesses at all as to the ratio between the observed and the unobserved universe? Could it be an infinite ratio?
Wait! We can't see all of the Universe; we don't know what is out there. The answer to the OP must be something akin to the answer to "how many angels can dance on the point of a needle".
late to this one but no. Einstein did not think of it as a geometry. He thought of it as a relativistic gravitational 'field'. In a similar way to how you can change your experience of a Electromagnetic field by your 'motion' relative it, a gravitational field also is observer dependent. It exist as long as you don't fall, as soon as you're in that free fall you negated it acting on you, locally defined. So he wanted to find a way to unify both into one field, as I understand it.Did he ever come around to thinking of it as a geometry?
Maybe not Geordie, maybe it's reaching a singularity. And that singularity by some reason seems to coincidence with our very possible demise, or survival. Depends on how much you trust the way we handled things so far? You're an optimist?It does seem like it is approaching a singularity but I suspect it is a mirage.
That is incorrect. Light is always moving when going into a black hole. It's merely slowing down. A particle like a photon can always be moving towards the event horizon and still never get there. Its sort of like Zeno's paradox. First its moving at c, then later at c/2 then c/4 then c/5 ....... At no time in that sequence is the photon at resDoes it follow from that that light slows down (from an observer's perspective) whenever it goes into any gravitational well (eg the Sun) ?
Even light slows down in a gravitational field and so too for photons moving towards the black hole.Does it slow down in a continuous way ?(ie if the gravitation increases it slows down more and more until the gravItational force is equal to that of a black hole and its speed is zero: do more powerful black holes make its velocity reverse?)
Pedant? Do you mean "dependent"?
But if relativity is to be believed, how could space be curved and relative from the point of the observer simultaniously ? Surely the observer should see a straight line space due to acceleration being relative ? I think pedant is the word.
But space is curved and that is why the path is the shortest distance, that being the curved motion from the point of view of the observer. Due to the acceleration of gravity being greater one side as compared to the other. They are under there own relative motion. Only question is which body is going under acceleration ?I think neither are since an accelerometer on either body will read zero.
What do you mean by " A "straight line" in GR is the shortest path.... " ?I haven't got around to reading your quotes (or PmbPhy's Wikipedia "model" page ) yet ,but I will soon)
Try the quotes I gave and see if they agree with it.
Maybe I did misread what you meant saying that " Isn't euclidean straightness an idealization ". The way I understood that sentence was in pointing out that it was a limited truth, much like Newtonian physics versus relativity? You need to define your thoughts again.
I don't think it was for Einstein geordief. The way I got it he didn't consider trajectories 'curved'. As I read him he thought of them as the shortest path, and how can the shortest path be curved? I know, you can argue the opposite, but that's what I got from reading him.Yes but those lines were not Euclidean ,were they?
" Already in the ﬁrst papers in which Einstein starts making use of the metric tensor to give an account of gravitation, he is at pains to establish the status of the geodesic equation as describing the motion of particles as “straight and uniform” (geradlinig und gleichförmig) even when subject to gravity. ... Einstein thought of (static) gravitational ﬁelds not as invariant force ﬁelds diverting particles from inertial motion. Already, in 1912, he thought of equation (1) as describing inertial motion on one hand, and as describing motion in the presence of (static) gravitational ﬁelds on the other. "
It's funny but even when not knowing this I wondered how SpaceTime would 'look' if 'folded out' into what we normally would call 'straight lines'. Which also lead me to wonder how many simultaneous 'geodesics' there could be at one point in the SpaceTime we see astronomically. The answer I got was innumerable.